Indicating plug fuse



May '3, 1934. F. c, LA MAR 1,957,546

INDICATING PLUG FUSE Filed Feb. 19, 1932 I Patented May 8, j

UNITED STATES PATENT OFF-ICE.

INDICATING PLUG FUSE Frank G. La Mar, New York, N. Y.

Application February 19, 1932, Serial No. 594,024

Claims. (Cl. 200-121 Thisinvention relates to electrical devices,parproduce a combined fuse and fuse integrity inticularly to thermalfuses for use in connection dicator which will be substantially the sameexwith electrical circuits, and more especially to temel dimensions asB- t derd D 18 what is known as a plug fuse, combined with Other objectsand advantages will pp 88 5 means for indicating the integrity of thefusible the description of the particular physical em- 60 element.bodiments selected to illustrate the invention It is quite universallyknown that it is necesprogresses, and the novel features will be parsaryto protect electrical circuits by means of deticularly pointed out inthe appended claims. vices, such as thermal fuses, which melt or be- Indescribing the invention in detail and the come disintegrated ordestroyed when an exces- Particular Physical embOdiments s c ed to 11-65 sive flow of current passes through the circuit of lustrate theinvention, reference will be had to which the fuse forms a part. Anespecially well the accompanying drawing and the several views knownform of thermal fuse is that known as thereon, in which like charactersof reference plug fuses". Ordinary plug fuses consist, gendesignate likeparts throughout the several views, erally, of an insulating body havingtwo terand in which: 70

minals on the outside thereof so constructed and Figure l is a top planview of a device embodyarranged as to be readily brought in contact withins appli an s inv n ion of a combined fuse and the terminals of anelectrical circuit, by way of fuse integrity indicator; Fig. 2 is anelevational what is known usually as a fuse block. These v w e de e as sown by Fig. 1; Fig. 3 is fuses are so universally used, and are made bya top plan view of applicant's device, as shown 76 so many differentmanufacturers, and must all .by 1. t wi h the p le indicating 9 beusable in practically any of the well known tion removed; Fi 4 is a p Pw 0 h forms of fuseblock, that they have become, in separabl indicatingp r of pp nt's intruth, standard, so that they may well be reventionwith the top cover removed; Fig. 5 is an ferred to as, standard, fuseplugs. At any rate enlarged elevational cross-sectional view of the 80they are substantially standard as regards their device a h wn by Fi 2;Fi 6 is n enlar ed v} I general external dimensions, elevationalcross-sectional view of the device as various forms of plugfuses havebeen made, Shown by taken on a p a at a ri h angle especially for thepurpose of enabling one to t th pla up n whi h Fi 5 is ta n; 7 israpidly discern whether or not the fusible or an vet al View, P y in566151011, 0f mpdithermal element is intact. It is quite the univerfied0 0f pp b ned fuse and fuse sal impression that success has not beenattained integrity indicator; Fig. 8 is an elevational crossin regard tothe feature of indicating the insectional view of another modified formembodytegrity of the fusible element. ing applicant's invention ofa-combined fuse and 35 A principal object of applicant's invention isfuse integrity indicator; Fig. 9 is a fragmentary to provide a device,which may well be called a elevational view illustrating the parts of aporcombined fuse and fuse integrity indicating detion of the device, asshownby Fig. 8. as viewed vice. In providing such a device, applicanthas from either side thereof as shownin Fig. 8; 10 had in mind that itpreferably should be in exis an elevational cross-sectional view ofanother 40 ternal dimensions substantially the size of the modified formof device embodying applicants standard plug fuse, so that it may beused with invention; Fig. 11 is an elevational cross-sectional afacility equal to that of a plug fuse in those view of the device asshown by Fig. .10, but taken situations where a plug fuse is now used.upon a plane at a right angle to the plane upon A further object whichapplicant has in mind which the view, Fig. 10, is taken.

45 in producing his combined fuse and fuse integrity The partscorresponding to the parts of the indicator is that the cost must bereduced to a ordinary standard plug fuse are well illustrated pointwhere, if possible, it approximates the by Figs. 2 and 5. Just as in thedevice illustrated present cost of ordinary plug fuses. To this in Figs.2 and 5, the ordinary plug fuse includes end, applicant has, as afurther object of his 'abody of insulating material, generally hollow,1;

invention, the production of a device in two parts, a, threaded metallicshell or terminal 2 attached separable one from the other, one partperformto the body; a metallic button or terminal 3; a ing the functionsnow performed by the ordinary metallic conductor 4 and a metallicconductor 5, plugfuse, and the otherpart performing the inone inelectrical contact with the terminal 3, and dicating functions desiredby applicant. the other in electrical contact with the threaded 55 Afurther object of applicant's invention is to shell terminal 2, both ofwhich at some portion mal element 8 connecting the members 4 and 5 atthe points 6 and 7 respectively. All of the parts hereinbeforedescribed, arranged substantially as shown, are common and ordinarilyfound in the ordinary standard plug fuse. The ordinary standard plugfuse includes an enlarged portion 9 forming the manually manipulativeportion of the plug fuse, by which it is grasped when it is screwed intoa fuse block for insertion in an electrical circuit.

Applicants device contains not only all of the parts as hereinbeforedescribed, but in addition has the metallic contact members 10 andllpositioned at the open upper end of the plug and connected electricallyrespectively with the conducting members 4 and 5. Applicant's devicecontains a shield 12, preferably of insulating material, such asisinglass or mica, held removably in place by the spring ring 13positioned in a groove of the body. The ordinary standard plug alsoincludes a shield corresponding to applicant's shield 12, although it isgenerally placed in a diflerent position, but functions substantially asapplicants shields function, that is, it prevents molten metal orextremely hot vapor from being projected without the hollow. of the body1 when the fusible or thermal element 8 is destroyed by an excessiveflow of current.

A device embodying all of the parts hereinbefore described. wouldconstitute an efficient and practicable plug fuse and could be so used,but in order to ez'hibit applicants invention, there must be a-fuseintegrity indicating means in addition.

The fuse integrity indicating means of appplicant may be of variouskinds, but applicant prefers an electric lamp 14, and preferably a distinctive indication lamp, such for instance, as a neon filled lamp, orthe glow type, operated by an electrical discharge within the lamp, sothat when lighted it will give an arrestive indication even in thepresense of white or yellow light as commonly used for illumination. Theelectric lamp, whatever its form, will generally and preferably have twoterminals as 15 and 16. These terminals will be electrically andmechanically connectedto metallic prongs as 17 and 18 through a resistor35 of suitable value and form, such, for instance, as the well knowngrid leak type. The prongs 17 and 18 will be so formed that they areadapted to cooperate with the metallic contact members 10 and 11, thatis, the prongs 17 and 18 will make mechanical and electrical contactwith metallic contacts 10 and 11 so that thereby the lamp 14 is in ashunt circuit to the thermal element 8.

Applicant prefers to mount the lamp 14 and the metallic prongs, as 17and 18, in a hollow disc like structure 19. This structure is made ofinsulating material and has a substantially fiat surface 20 withapertures, as 21, therein so that the light from lamp 14 may shinetherethrough.

" The bottom 22 of the disc 19 is formed of a portion of insulatingmaterial cemented or otherwise properly attached to the annulus 19 ofthe disc and supports, mechanically, in separated position, the metallicprongs, as 17 and 18. The hollow disc 19 is preferably made of suchdimension, vertically, as shown in Fig. 5, that it adds a minimum to thetotal length of the plug, at

any rate it does not add an amount sufiicient to ordinarily prevent thecombined device from being used in those positions where an ordinarystandard plug fuse now may be used.

As some strain may be put upon disc 19 in turning the plug into itssocket, applicant has provided that the disc 19 shall fit into an ovaldepression 23 of the hollow body 1. The wall of this oval depressionsupports the disc 19 so that if strain is placed thereon, the prongs l7and 18 will not be obliged to stand the strain.

In Fig. 7 applicant has shown a modification, in that the separableindicating portion 24 is made in the form of a tube within which ispositioned the lamp 14, and to the metallic ends 25 and 26 to which areconnected the terminals 15 and 16 of the lamp. The metallic end pieces25 and 26 are attached to metallic prongs 17 and 18, just as are shownin Fig. 5, and these prongs function exactly as do the prongs of Fig. 6.In order to prevent strain upon the prongs l7 and 18, in the form asshown by Fig. 7, applicant places the tube 24in a slight recess of theboth! 28, corresponding approximately in function to the recess 23 ofbody 1 of Fig. 1.

In Fig. 8, applicant has shown a further modified form of the deviceembodying his invention. In this form the disc 19 is let into the tubeof the body portion 29 corresponding to the body portion 1 of Fig. 2 tosuch an extent that the top of the disc 19 is flush with the top of thebody 29. Applicant illustrates nail spaces 30 and 31 for the insertionof the nail of the finger for the purpose of removing the disc 19.

In Figs. 10 and 11, applicant has illustrated a further modified form ofthe invention. In this form the body portion is formed in two parts, alower part 31 and an upper part 32, the combined length being that ofthe standard plug fuse,-

the separation being made along the line 33.

In the form as shown by Figs. 10 and 11, the portion 32 correspondingwith the disc 19 of Fig. 5 has a cover portion 20 which is held in placeby a spring ring 34, thereby enabling one to more readily get to thelamp 14.

From the hereinbefore given description, it will be seen that applicanthas provided a combined fuse and fuse integrity indicator formed of twoseparable parts, one of which corresponds with and is capable ofperforming all of the functions of the ordinary standard plug fuse, theother of which combined with the first mentioned part serves to indicatethe integrity of the thermal element proper, in that when the thermalelement proper is destroyed the indicating means will show such facts bythe lighting of a lamp.

It is further apparent that all forms of applicants combined device aresuch that each has an over-all lengtlnot too great to successfully allowthe use in those positions in which the ordinary standard fuse is nowused, if one bears in mind, that in practically all cases, some slightallowance is made between the end of an ordinary standard plug fuseblock and the cover ordinarily used to protect it.

It is further seen that some of applicants forms,

originally and previously used may be combined with the new thermalelement portion.

Although I have particularly described several particular physicalembodiments of my invention and explained the operation, constructionand principle thereof, nevertheless, I desire to have it understood thatthe forms selected are merely illustrative, but do not exhaust thepossible physical embodiments of the idea of means underlying myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In a plug fuse, in combination: an insulating hollow body; twoterminals on the outside of the body for cooperation with terminals ofan electrical circuit to be protected; two combined conducting andmechanical connecting members,

each connected electrically to one of the terminals, at least, partiallyexposed within the body; a thermal element connecting said twoconducting members; said conducting members forming contact terminalsfor cooperation with the contact terminals of a separable thermalelement integrity indicator; 8. thermal element integrity indicator andmechanical connecting means for attaching the integrity indicator to thehollow body cooperating with the said two combined conducting andmechanical connecting members.-

2. A combined thermal fuse and fuse integrity indicator consisting of aplug portion and a separable indicating portion; the plug portioncomprising an insulating body provided with two terminals forcooperation with terminals of an electrical circuit to be protected, 8.thermal portion connecting the first mentioned terminals, and twocombined metallic electrical and mechanically attaching contacts, oneconnected to each of the first mentioned terminals; the separableindicating portion including an indicating electric lamp provided withtwo terminals and two combined metallic electrical and mechanicallyattaching members, one connected to each of the lamp terminals, forattaching the indicating portion to the plug portion mechanically andelectrically connecting the metallic contacts of the plug portion to themetallic members of the indicating portion and a housing for the lampformed substantially as a hollow disc with observation slits therein.

3. A combined'thennal fuse and fuse integrity indicator consisting of aplug portion and a sepa rable indicating portion; the plug portioncomprising an insulating body provided with two terminals forcooperation with terminals of an electrical circuit to be protected; athermal portwo metallic contacts, one connected to each of the firstmentioned terminals; the separable indicating portion including adistinctive indication indicating electric lamp provided with twoterminals and two metallic members, one connected to each of the lampterminals, for attaching the indicating portion to the plug portion andelectrically connecting the metallic contacts of the plug portion to themetallic members of the indicating portion and substantially a hollowdisc formed with observation slits for housing the lamp.

4. A combined fuse and fuse integrity indicator formed of two separableparts; one part having substantially the form and shape of the lower onehalf terminal end of a standard plug fuse and supporting and containingterminals and a thermal element connecting the terminals and in additiontwo metallic contacts adjacent the open end; and theother portioncorresponding to the upper or manually grasping and manipulating half,separable from the other half, and supporting and containing anindicating lamp having metallic members connected to the terminalsthereof for contact with the metallic contacts carried by the other halfwhereby the whole may be used and positioned for use in the same manneras an ordinary plug fuse but when the thermal element of the fusebecomes destroyed the lamp will light and when renewal of the thermalelement is accomplished the original separable indicating lamp portionis used therewith.

5. A fuse integrity indicator formed substantially as a hollow disc withapertures open ng in one flat surface; an indicating lamp provided withterminals within the hollow of the disc; and two separated metallicprongs projecting from the substantially fiat surface of the discopposite the surface in which the apertures are formed, one of themetallic prongs being connected to one terminal of the lamp, and theother prong being connected to the other terminal of the lamp, saidprongs adapted to contact and make electrical connection with the endsof a fusible element of an electrical circuit thereby placing the lampin shunt to said fusible element whereby upon the destruction of thefusible element the lamp will be lighted to indicate the disruption ofthe fusible element.

FRANK C. LA MAB;

tion connecting the first mentioned terminals, and

